1. Field of the Invention
The present invention relates to an optical near-field generator and a recording and reproduction apparatus including a head having an optical near-field generator mounted thereon.
2. Description of the Related Art
Thermally assisted magnetic recording has recently been proposed as a recording system for achieving a recording density of 1 Tb/in2 or higher. With a recording density of 1 Tb/in2 or higher, conventional magnetic recording apparatuses have a problem that thermal fluctuations destroy recorded information. The prevention of this requires enhancement of coercivity of a magnetic recording medium. Too high a coercivity, however, makes it impossible to form a record bit on the medium, because there is a limit to the magnitude of the magnetic field that a recording head can generate. To solve this, in the case of the thermally assisted magnetic recording, the coercivity is reduced at the instant of recording by heating the medium with light. This makes it possible to record on media with high-coercivity, and thus to achieve a recording density of 1 Tb/in2 or higher.
For the thermally assisted magnetic recording apparatus, it is necessary that the spot size of light to be irradiated be substantially equivalent to the size of the record bit (e.g., a few tens nm). The reason is that the spot size of light in excess of a few tens nm erases information on an adjacent track. An optical near-field is used to heat such a minute region. The optical near-field is a local electromagnetic field (or light of which the wave number contains imaginary components) that is present in the vicinity of a minute object equal to or smaller than wavelengths of light. A microaperture having a diameter equal to or smaller than the wavelengths of light or a metallic scatterer is used to generate the optical near-field. An optical near-field generator using a metallic scatterer of a triangular shape is proposed as a high-efficiency optical near-field generator in Technical Digest of 6th international conference on near field optics and related techniques, the Netherlands, Aug. 27-31, 2000, p 55, for example. When light enters the metallic scatterer, plasmon resonance is excited in the metallic scatterer, and a strong optical near-field is generated on a vertex of the triangle. Using this optical near-field generator makes it possible to focus light with high efficiency on a region equal to or smaller than a few tens of nanometers.
The thermally assisted magnetic recording apparatus uses a magnetic reproduction element, such as a giant magnetoresistive (GMR) element or a tunneling magnetoresistive (TMR) element, as means for reproducing which reproduces recorded information (see H. Saga, H. Nemoto, H. Sukeda, and M. Takahashi, Jpn. J. Appl. Phys. 38, Part 1, 1839 (1999)). However, an optical near-field may be utilized as the reproduction means, in place of the magnetic reproduction element. For example, there is a report on an experiment in which a mark recorded on a magnetic medium is reproduced by monitoring the rotation of polarized light (see E. Betzig, J. K. Trautman, R. Wolfe, E. M. Gyorgy, P. L. Finn, M. H. Kryder and C.-H. Chang, Appl. Phys. Lett. 61, 142 (1992)). There is also a report on an experiment in which a mark recorded on a phase change medium is reproduced by monitoring a change in the intensity of reflected light (see S. Hosaka, T. Shintani, M. Miyamoto, A. Kikukawa, A. Hirtsune, M. Terao, M. Yoshida, K. Fujita, S. Krammer, J. Appl. Phys. 79, 8082 (1996)).